MnDOT Contract No. 99741
Exhibit A
Scope of Services
Ground penetrating Radar for Bridge Deck Inspection
Contractor will perform bridge deck inspections using ground penetrating radar (GPR). The description of the work and GPR specifications are as follows. Where minor detail of the Contractor’s equipment differ from those stated in theses specifications, the Contractor may use equivalent equipment. Specific bridges are undetermined at this time, but MnDOT currently expects to inspect 50 to 75 bridges with the potential of an accumulated deck square footage of 1,000,000 square feet.
Ground Penetrating Radar
The GPR will consist of an array of non-contacting antennas and must be capable of high speed inspection of bridge decks for delaminations and deteriorated concrete, measurement of rebar depth and overlay thickness. The antennas will be spaced three feet apart permitting full 12-foot lane coverage in a single vehicular pass. The GPR system will be installed in a vehicle and the inspection conducted at highway speed of 45 mph, thereby probably eliminating the need for maintenance and protection of traffic.
Standards and Guidelines
The GPR inspection will be conducted in compliance with:
· American Association of State Highway and Transportation Officials (AASHTO) test method TP-36 “Standard Test Method for Evaluating Asphalt-Covered Bridge Decks using Pulsed Radar”, incorporated by reference.
· American Society for Testing and Materials (ASTM) D6087-97/03 “Standard Test Method for Evaluating Asphalt-Covered Bridge Decks using Ground Penetrating Radar”, incorporated by reference.
· Strategic Highway Research Program (SHRP), SHRP Project C-101 Task B for research for detection of deterioration in asphalt covered concrete decks, incorporated by reference.
Ground Penetrating Radar Apparatus
The GPR system will consist of the following components:
Ground Penetrating Radar
· The GPR will be a digital, touchscreen-controlled system with non-contacting horn antennas, synchronized for simultaneous operation.
· Each antenna will transmit a 1.0 nanosecond monocycle signal at a 5 megahertz pulse repetition frequency.
· Each antenna will operate with a range scan of 15 nanoseconds and a range scan scale of 100 scans per second minimum.
· The radar equipment will employ an Autolock capability to automatically lock and stabilize the surface reflection against antenna bounce.
· The radar equipment will employ a digital subtraction technique to improve signal quality by digital removal of internal system noise known as clutter.
Data Acquisition System
· A data acquisition system will consist of equipment for collecting radar data at a minimum rate of 80 kilohertz for each antenna.
· To ensure maximum longitudinal deck coverage, the data acquisition system will be capable of acquiring every radar range scan from all antennas simultaneously without loss of data.
· The data acquisition system will be capable of digital radar acquisition at speeds of 45 mph and storage for radars to the hard disk for continuous periods of no less than eight hours.
Distance Measurement System
· A distance measurement system consisting of an appropriate distance measurement instrument with an accuracy of +/- 100 millimeters per kilometer (+/- 6.5 inches per mile) and a resolution of 25 millimeters (1 inch) will be used to register GPR data relative to traveled distance. The GPR will be capable of acquiring Global Positioning Satellite information.
Test Vehicle
· The GPR vehicle must be capable of carrying front-mounted GPR antennas and operating at highway speed.
· The vehicle must be installed with all equipment necessary to perform the test and will also include proper warning and safety devices installed.
· The vehicle will contain autonomous power sufficient to power the GPR equipment.
Test Conditions
The bridge decks must be relatively clean of soil, aggregate or other particulate debris, and must be in a surface-dry condition.
Ground Penetrating Radar Data Collection
· The radar inspection will be performed in a series of longitudinal passes along the length of the bridge deck using an array of air-coupled GPR antennas.
· The antenna array will be positioned on the front of the inspection vehicle with a fixed spacing of 36 inches (91 centimeters) between antennas to ensure registration of radar passes and ensure full lane coverage.
· Longitudinal radar passes will be made in a continuous manner along the length of the deck and accurately spaced 36 inches +/- 3 inches (91 centimeters +/- 7.6 centimeters) apart in the transverse direction. A sufficient number of passes will be made to cover the width of the bridge deck.
· The survey will be performed in all traffic lanes in the direction of traffic, and at no times will the GPR vehicle be permitted to straddle lanes during data collection.
· Each vehicle pass will simultaneously collect antenna passes. A sufficient number of passes will be made to cover the width of the bridge deck.
· Distance will be maintained through use of a vehicle-mounted, precision distance measuring instrument and GPS
· The GPR inspection will be conducted at highway speeds (45+ miles per hour) or at the posted speed, whichever is lower. This will minimize interference to traffic and eliminate the need for maintenance and protection of traffic.
Data Collection Procedure
· Initial setup and calibration or radar equipment: This involves installation of antennas and measurement of known calibration targets including flat metal plate reflector and free space.
· Analyze the bridge deck dimensions and identify the location of the radar inspection scans.
· Collect GPR data while simultaneously acquiring antenna scans per traffic lane.
· Conduct a visual examination of the bridge deck, documenting and if possible, photographing representative areas of distress.
Ground Penetrating Radar Data Analysis
All GPR data will be analyzed for delamination at the top reinforcing steel layer, in accordance with AASHTO TP36 and ASTM D6087-97/03 based upon measurement of signal attenuation through the concrete deck. Algorithms and software developed under SHRP C101, such as IRIS BridgePro, will be used for analysis. Areas of delamination at the top rebar will be presented graphically in plan view mappings.
Optionally, the GPR will be analyzed for the following:
· Delamination at bottom reinforcement. For bridge decks where bottom spalling is likely to occur, the GPR data will be analyzed for delamination at the bottom rebar. Areas of delamination at the bottom rebar will be presented graphically in plan view mappings.
· Debonding. For decks with concrete or latex modified concrete overlays, all radar data will be analyzed and the locations of debonded overlay will be determined and presented graphically in plan view mappings.
· Scaling (freeze-thaw damage). For decks with a bituminous overlay, all radar data will be analyzed and the locations of freeze-thaw damaged concrete will be identified and presented graphically in plan view mappings.
· Depth of Reinforcement. All radar data will be analyzed and reinforcement depth will be determined and presented graphically in a color topographical plan view and in numerical format.
· Asphalt overlay thickness. For decks with a bituminous overlay, all radar data (every radar scan) will be analyzed and asphalt thickness will be determined and presented in a color topographical plan view, and in numerical tabulated format.
Traffic Control
If required, Contractor will be responsible for all traffic control. Traffic Control will be in accordance with the following standards.
· Manual on Uniform Traffic Control Devices (MUTCD)
· Temporary Traffic Control Zone Layouts
· Work Zone Field Handbook
· Guide to establishing Speed Limits in Highway Zones
· Minnesota Flagging Handbook
· Provisions of Mn/DOT 1404 and 1710
· Minnesota Standard Signs Manual
· Traffic Engineering Manual
· Traffic Control Layout
See web site: http://www.dot.state.mn.us/trafficeng/otepubl/index.html
Contractor will call in any lane closures to dispatch 511 and submit the standard form.
In unique situation that include large volumes, signalized intersections or if the highway is not in the Lane Closure Manual, contact Metro Traffic Engineering, Work Zone.
Deliverables
Contractor will provide, for each bridge, a written report on the results of the GPR inspection. The report will include an executive summary, description of the test procedure and equipment, technical discussion and an overall discussion of the GPR findings.
In the event inspection or analysis reveals a significant safety concern, Contractor will notify the State immediately and a report will be submitted as soon as possible.
The final report will include a plan view layout of each bridge deck, in hardcopy and electronic (PDF) format on disk, graphically showing areas of delamination. The overall percent of delaminated deck concrete will also be reported. The report will include photos showing elevations, cracks and observations. The report will also designate the location and quantity of concrete that should be removed (type 2 repairs) in square feet.
Two hard, bound, copies of the final report will be submitted for each bridge deck and one compiled copy of all bridges, along with two CD copies of the completed report.
Optionally, a plan view map of the bridge will be produced in hardcopy and electronic (PDF) format showing
· Areas of concrete that are delaminated at the bottom rebar,
· Areas where the LMC or concrete overlay is debonded,
· Areas of asphalt covered concrete exhibiting freeze-thaw damage (scaling)
· Asphalt thickness and depth of reinforcement, where applicable.
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